P. Millburn

The Fate of [14C]Phenol in Various Species

1. [14C]Phenol has been administered to man (dose, 0.01 mg/kg) and 18 animal species (25 mg/kg) and the urine examined for metabolites by radiochromatogram scanning.2. In three men 90% of an oral dose was excreted in 24 h mainly as phenylsulphate (77% of 24 h excretion) and phenylglucuronide (16%) with very small amounts of quinol sulphate and glucuronide.3. Four metabolites, the sulphates and glucuronides of phenol and quinol, were found in the urine of the rodents, the rat, mouse, jerboa, gerbil, hamster, lemming and guinea-pig after an oral dose of phenol.4. Three metabolites were excreted by some species, namely, phenol and quinol glucuronides and phenylsulphate by the squirrel monkey and capuchin monkey, and phenol and quinol sulphates and phenylglucuronide by the ferret, dog, hedgehog and rabbit.5. Two metabolites were excreted by the rhesus monkey, fruit bat and hen (phenylsulphate and phenylglucuronide) and by the cat (phenylsulphate and quinol sulphate). One metabolite (phenylglucuronide) only wa...

Bile and Urine as Complementary Pathways for the Excretion of Foreign Organic Compounds

1. The urinary and biliary excretion in the rat of 30 aromatic compounds with mol. wt. of 100-850, and largely excreted unchanged, has been studied. 2. These compounds fall into three groups as regards their pattern of elimination, which is related to mol. wt: group 1, with mol. wt. less than 350 and the major route of elimination the urine. When urinary excretion is prevented by ligating the renal pedicles the biliary excretion remains low. group 2, with mol, wt. of 450-850 which are excreted predominantly in bile. Even when the bile duct is obstructed, only small amounts of these compounds are found in urine. group 3, with mol. wt. of 350-450, which are eliminated extensively in both urine and bile. When one of these routes is blocked excretion by the other increases. 3. These studies emphasize the interrelationship of urine and bile as excretory routes for organic compounds. Urine and bile are complementary pathways; the extent of urinary excretion is greatest for the compounds of lowest mol. wt. and tends to decrease as mol. wt. increases and biliary excretion becomes more extensive.

The biliary excretion and enterohepatic circulation of benzo (a)pyrene and its metabolites in the rat

Abstract The enterohepatic circulation of benzo( a )pyrene (BP) has been investigated in the rat with a view to determining the availability of potentially toxic metabolities to tissues within this cycle. Some 60% of the dose of [ 14 C]-BP (3 μmoles kg −1 , i.v.) is excreted in bile in 6 hr, with less than 3% in urine. The biliary metabolities are mainly polar conjugates; only 8% of the 14 C in 2 hr bile samples can be directly extracted into ethyl acetate. However, following hydrolysis by β-glucuronidase some 40% of the 14 C is extractable at pH 7. The extract consisted of polar metabolites (polyhydroxylated and/or conjugated; 37.5%), BP 4,5-diol (16.8%), BP 3,6-quinone (5.9%). 9-hydroxy BP (5.4%) and 3-hydroxy BP (5.3%) as indicated by co-chromatography with authentic standards on reversed phase HPLC, together with several unidentified metabolites. The proximate carcinogen BP 7, 8-diol was not detected. Biliary metabolites of [ 14 C]-BP undergo enterohepatic recirculation in the rat; following the intraduodenal infusion of bile containing metabolites of [ 14 C]-BP into bile duct cannulated rats, approximately 20% of the dose is absorbed and excreted in bile in 30 hr, with only 1% in urine. The pattern of metabolites in this bile is very similar to that in bile from rats administered [ 14 C]-BP i.v. Following a single i.v. dose of [ 14 C]-BP (3 μmoles kg −1 ) to rats with re-entrant bile duct cannulae, which allowed intermittent collection of bile over a period of several days with minimal interference to the enterohepatic circulation, the proximate carcinogen BP 7, 8-diol was detected in recirculating bile. Biliary metabolites of BP, which have recently been shown to be mutagenic, can thus traverse the intestine to undergo enterohepatic circulation in the rat.

The Conjugation of 1- and 2-Naphthols and other Phenols in the Cat and Pig

[1-14C]-Naphthol and [8-14C]2-naphthol (25 mg/kg) injected into cats were excreted in the urine almost entirely as sulphate conjugates. Only about 1–2% of the dose appeared as naphthylglucuronides. 1-Naphthol gave entirely 1-naphthylsulphate whereas 2-naphthol gave 2-naphthylsulphate and an unidentified hydroxynaphthylsulphate in the ratio of 4 : 1.When [8-14C]2-naphthol was injected into pigs (dose 25 mg/kg) it was excreted mainly as 2-naphthylglucuronide with a small amount of 2-naphthyl sulphate (ratio about 15 : 1), but when [1-14C]1-naphthol was injected, 1-naphthylglucuronide and 1-naphthylsulphate were excreted in the ratio of 2 : 1. The pig, therefore, formed substantial amounts of 1-naphthylsulphate but not of 2-naphthylsulphate.The cat excreted injected [14C]morphine mainly as morphine 3-sulphate and [14C]phenacetin as 4-acetamidophenylsulphate, but injected [3H]phenolphthalein was excreted as the glucuronide and sulphate in the ratio of 3 : 2. The cat, therefore, formed substantial amounts of p...

Enterohepatic recycling of phenolphthalein, morphine, lysergic acid diethylamide (LSD) and diphenylacetic acid in the rat Hydrolysis of glucuronic acid conjugates in the gut lumen

1. Biliary elimination in female Wistar albino rats 3 h after i.p. injection of [3H]phenolphthalein, [3H]morphine, 14C-LSD and [14C]diphenylacetic acid was 90%, 45%, 75% and 57% respectively, predominantly as glucuronides. 2. Infusion of 3 h bile from the previous experiments into the duodena of bile-duct-cannulated animals demonstrated enterohepatic circulation, amounting in 24 h to 85%, 41%, 28% and 66% of the infused doses of the conjugates of phenolphthalein, morphine, LSD and diphenylacetic acid respectively. 3. Pretreatment with antibiotics to suppress intestinal microflora decreased this enterohepatic recirculation to 22%, 8.6% and 21% in 24 h for phenolphthalein, morphine and diphenylacetic acid glucuronides respectively. Antibiotic pretreatment did not influence the absorption and re-excretion of infused doses of the free aglycones, thus demonstrating the importance of bacterial beta-glucuronidase hydrolysis of the biliary conjugates. 4. The extent of intestinal absorption of the aglycones after bacterial beta-glucuronidase hydrolysis of the conjugates is related to their lipid-solubility as estimated by octan-1-ol:0.1 M phosphate buffer partition ratios (P-values). 5. The persistence of compounds in the enterohepatic circulation is determined by the faecal and urinary elimination of the circulating compounds. Faecal elimination is governed by the extent of intestinal absorption of the circulating compounds, which is influenced by the efficacy of intestinal hydrolysis of the conjugates and the relative lipophilicity of the aglycones released.

The role of the hepatic endoplasmic reticulum in the biliary excretion of foreign compounds by the rat: The effect of phenobarbitone and SKF 525-A (diethylaminoethyl diphenylpropylacetate)

Abstract Phenobarbitone pretreatment of rats stimulated the biliary excretion of biphenyl, stilboestrol and phenolphthalein all of which undergo metabolism prior to excretion in the bile. However, this treatment did not aflect the biliary elimination of stilboestrol glucuronide, phenolphthalein glucuronide, succinylsulphathiazole and indocyanine green all of which are excreted unchanged. SKF 525-A which inhibited the glucuronide conjugation of stilboestrol and phenolphthalein depressed their excretion in the bile in the form of their O-glucuronides. SKF 525-A did not influence the biliary excretion of phenolphthalein glucuronide. The biliary excretion of compounds such as biphenyl, stilboestrol and phenolphthalein can be considered to occur in at least two steps: (i) metabolism and (ii) transfer of the metabolites to bile. Phenobarbitone and SKF 525-A treatment in rats influences (i) but not (ii). This suggests that although the endoplasmic reticulum is involved in the metabolism of foreign compounds it does not appear to play a role in their transfer from liver to bile.

The Influence of Dose on the Pattern of Conjugation of Phenol and 1-Naphthol in Non-Human Primates

1. The pattern of conjugation of phenol and 1-naphthol was investigated in several primates; three Old World species (rhesus, cynomolgus, patas monkeys), two New World species (capuchin, tamarin), and two prosimians (bushbaby, tree shrew). 2. Following intra-muscular phenol or 1-naphthol (10 mg/kg), sulphation was the major conjugation in the Old World monkeys and prosimians, whereas glucuronidation predominated in the New World species. 3. In rhesus and cynomolgus monkeys, sulphation decreased as dose increased, but remained the major conjugation with both substrates at dose levels of 0.01 to 25 mg/kg. 4. In the capuchin, the conjugation pattern of phenol changed markedly as dose increased; at 0.01 and 1 mg/kg sulphation was the major conjugation, whereas at 10 and 25 mg/kg glucuronidation predominated. With 1-naphthol only small amounts of sulphate were excreted; glucuronic acid conjugation was the major metabolism at all four dose levels. 5. The importance of considering both substrate and dose when making inter-species comparisons, particularly with man, is discussed.

Taurine Conjugates as Metabolites of Arylacetic Acids in the Ferret

1. The pattern of conjugation in the ferret of 8 arylacetic acids and, for comparison, benzoic acid and 4-nitrobenzoic acid was examined. 2. The arylacetic acids, phenylacetic, 4-chloro- and 4-nitro phenylacetic, alpha-methylphenylacetic (hydratropic), 1- and 2-naphthylacetic and indol-3-ylacetic acids, were excreted in the urine as taurine and glycine conjugates. Diphenylacetic acid did not form an amino acid conjugate and was excreted as a glucuronide. 3. The taurine conjugate was the major metabolite of 4-nitrophenylacetic, alpha-methylphenylacetic, 1- and 2-naphthylacetic and indol-3-ylacetic acids, whereas the glycine conjugate was the major metabolite of phenylacetic and 4-chlorophenylacetic acids. Taurine conjugation did not occur with benzoic and 4-nitrobenzoic acids which were excreted as glycine and glucuronic acid conjugates. 4. Phenacetylglutamine and 4-hydroxyphenylacetic acid were minor urinary metabolites of phenylacetic in the ferret. 5. A number of taurine conjugates of aliphatic and aromatic acids were synthesized and their characterization and properties were studied. The role of taurine as an alternative to glycine in the metabolic conjugation of arylacetic acids is discussed.

Molecular Weight and Chemical Structure as Factors in the Biliary Excretion of Sulphonamides in the Rat

1. Biliary excretion in biliary-cannulated female rats of 23 derivatives of sulphanilamide, in which the N4-position is substituted with various carboxyacyl groups and the N1-position with acetyl or 2-thiazole, has been studied.2. Six compounds having molecular weights in the range 172–314 were poorly excreted in the bile ( 5–10% of dose).3. Above the threshold mol. wt., biliary excretion is high (20–70% of dose) but there is no direct relationship between the two, as the extent of biliary excretion is not directly proportional to mol. wt.4. There is no direct relationship between the extent of biliary excretion and the relative lipid solubilities as measured by distribution ratios between buffer pH 7.4 and organic solvents. Nevertheless th...

The Conjugation of Indolylacetic Acid in Man, Monkeys and other Species

Indol-3-yl[2-14C]acetic acid has been administered to 18 species of animals including man, and the urinary metabolites examined by radiochromatogram scanning. Man received 500 mg orally and the other animals 100 mg/kg by intraperitoneal injection.In most species, 50–90% of the administered 14C was excreted in the urine in 48 h. 14–76% of the indolylacetic acid was excreted unchanged in 48 h.In man, the 14C excreted in 48 h consisted of about 50% unchanged indolylacetic acid, 30% indolylacetylglucuronide and 10–20% indolylacetyl-glutamine. No glycine conjugate was detected.The glutamine conjugate was excreted only by the Old World (3 species) and New World (3 species) monkeys and man.The glycine conjugate was excreted by all species (13) except man, Old World monkeys and the pigeon. The three species of New World monkeys formed both the glutamine and glycine conjugates.Taurine conjugation of indolylacetic acid was studied in the green monkey, the squirrel monkey, the capuchin monkey, the ferret and pigeon....